Progress on a gridded electron gun for a sheet beam klystron

Summary form only given. Calabazas Creek Research, Inc.(CCR) is developing rectangular, gridded, thermionic, dispenser-cathode guns for sheet beam devices. The first application is expected to be klystrons for advanced particle accelerators and colliders. In this device, the beam has a rectangular cross section. The thickness is constrained as it would in a normal, cylindrically symmetric klystron with a Pierce gun. However, the width of the beam is many-times the thickness, and the resulting cross sectional area is much larger than in the conventional device. This allows much higher current and/or a lower voltage before space charge forces become too high. The current program addresses issues related to beam formation at the emitter surface, design and implementation of shadow and control grids in a rectangular geometry, and the high voltage insulator. It is directed toward a robust, cost-effective, and reliable mechanical design. A prototype, device will be developed that will operate at 415 kV, 250 A for a 40 MW, X-Band, sheet-beam klystron. The cathode will have 100 cm/sup 2/ of cathode area with an average cathode current loading of 2.5 A/cm/sup 2/. For short pulse formation, the use of a grid was chosen. The design of the electron gun was reported previously. The gun is designed to operate with DC voltages with the beam controlled by a tungsten grid. Diversified Technologies, Inc. is developing the power supplies under a related DOE-funded program. DC operation at 415 kV is a challenge, particularly since the insulators will be in oil, and current research is focusing on design of the insulator stack. The larger insulators are 43 cm in diameter. The maximum electric field in oil and vacuum are 35 and 50 kV/cm, respectively. These are expected to be acceptable, but the unit will be tested separately from the gun to verify the computer simulations. Fabrication of the gun is expected by fall 2004. Details of the final design of the diode and insulator will be di- cussed.